Why alloc_super use a static variable default_op?the static struct super_operations default_op is just all zeros, andjust referenced as the initial value of a new allocated super_block,what does it for?

the filesystem dependent code such as ext2_fill_super would fill thisfield eventually,and after carefully checked, it seems no one filesystem would need aall zero default_op,

as the command output in the kernel source tree:$ grep -RInw s_op fs/You could check all the use of s_op.